The people who work in committee or personal offices on Capitol Hill can claim something of a unique benefit from representative democracy: They have more than one set of members to call their own.

Their allegiances aren’t only to the senator or House member, chairman or committee members who keep them on the payroll. Those lawmakers may dominate their workaday lives, but every such staffer is also a local congressional constituent — with a set of political allegiances and ideological interests that may well be different from what’s on display in their day jobs.

And this year, more than any other time in at least the past two decades, these Hill rats will be important players in deciding the makeup of the next Congress. That’s because thousands of them will be voting in three of the hottest contests of the midterms, for the pair of open House seats in northern Virginia and the state’s Senate race, which Republicans hope will become competitive.

Most congressional aides probably live close to their work in the District, where Democrat Eleanor Holmes Norton is once again cruising toward another term (it will be her 13th) as the can’t-vote-on-the-House-floor delegate. Staffers who live in solidly blue suburban Maryland have seen only three congressional races that were even remotely close in the past decade.

But the booming Northern Virginia suburbs, fresh off their star turn as gubernatorial must-wins in 2013 and presidential bellwethers in both 2008 and 2012, are now looking at a very expensive triple encore in 2014. Commuters who cross the Potomac for jobs at the Capitol could prove decisive if all three contests remain close until their climaxes.

And they will all probably have the opportunity to vote for someone who knows their line of work: former Hill staffers are running as Republicans in all three races. The stage was set last weekend in the contest that — for now, at least — looks to remain the closest until November, the House seat covering the commuter enclaves of Chantilly and Manassas, the palatial estates of northern Fairfax County and all of burgeoning Loudoun County.

Barbara Comstock, a Republican state delegate since 2010 and the choice of the party establishment , prevailed in an usual “firehouse” primary against five rivals who divided the vote of tea party and cultural conservatives. Her opponent is now Fairfax County Supervisor John Foust, unchallenged for the Democratic nomination. They are competing for the seat that Rep. Frank R. Wolf is relinquishing after 17 terms, and Comstock worked for him on the Hill in the early 1990s.

Virginia's 10th looks like the very definition of a swing district: Mitt Romney prevailed by a hair in 2012, but the same precincts preferred President Barack Obama by 4 points in 2008.

Thanks in part to the same reasons GOP candidates nationwide have the edge, starting with the president’s unpopularity, the race at the moment is leaning in Comstock’s favor .

But Foust and Comstock both raised more than $750,000 in the first 90 days of this year, suggesting theirs could be one of the most expensive House races in the nation. An expanding roster of defense contractors, technology firms and consultants (with billions in federal billings every year) have addresses near Dulles International Airport, the district’s economic heart. And their legions of white-collar professional workers have given the 10th the highest median income in the Old Dominion — more than $110,000, meaning many voters have disposable income available for making donations.

The timetable and partisan dynamic are totally different in the adjacent district to the south and east — covering Arlington, Falls Church, Alexandria and Mount Vernon. (The dividing line twists through the middle of McLean, still home to many of the capital’s political and advocacy elite.)

The election of a successor to Rep. James P. Moran, retiring after 24 years, will effectively be a done deal after the June 10 Democratic primary. That’s because it's overwhelmingly Democratic territory: 68 percent of the 8th District voted for Obama in both of his elections.

In a macro sense, the district is similar to its neighbor. Both are bustling and mostly affluent, the home of many well-paid federal workers, government contractors and the sorts of businesses that need to keep a keen eye on Congress. But the area Moran has represented is much closer to downtown Washington, so it has very few of the rolling greenswards and mansions found on Wolf’s turf, and many more people who live in apartment towers and take Metro to work. That’s helped to yield more demographic diversity; Moran’s 8th is 45 percent African-American, Asian or Hispanic, whereas Wolf’s 10th is only 30 percent non-white.

Eleven Democrats are running in the 8th District primary, but one seems to have a decided advantage based on his name identification, broad experience and fundraising clout. That's Don Beyer, the longtime star of the TV ads for his eponymous chain of Volvo dealerships, Virginia’s lieutenant governor from 1990 through 1997, Obama’s major campaign bundler and ambassador to Switzerland and Liechtenstein during Obama's tenure.

He raised $672,000 in the first three months of 2014 and began April with $450,000 in the bank — more than twice as much as his three closest fundraising rivals: radio host Mark Levine, former Navy pilot Bruce Shuttleworth and former Northern Virginia Urban League head Lavern Chatman. But each of them could claim more than $200,000 in cash on hand only because they’ve loaned or donated substantially to their own efforts. Beyer clearly has the capacity to do likewise, but so far hasn’t opted to be a self-funder.

The likeliest Republican nominee is aerospace industry lobbyist Micah Edmond, who has worked for several House Armed Services Committee members. He raised only $44,000 this year, reason enough to suspect he won’t put up much of a fight in November.

The most expensive race in Virginia, however, will surely be the Senate contest. Democratic Sen. Mark Warner, the former governor, remains the clear but hardly prohibitive favorite. Helped by his new seat on the Finance Committee, he raised $2.7 million in January, February and March and began April with $8.8 million in his campaign account. But the lobbyist and former Republican National Committee chairman Ed Gillespie, who got his big political boost working for the House leadership in the 1990s, has raised $2.2 million just since announcing his bid in January. That's an amount that suggests he’ll have the resources to sell his message.

All this is before candidate fundraising and spending, and waves of independent expenditures, shift into overdrive. Once the television advertising and direct mail onslaughts begin, there will be one more reason why this campaign season is unusually meaningful for so many Hill staffers: For evidence about what happens at the intersections of big money, politics and congressional policymaking, many aides won’t even have to leave home.